1. Field of the Invention
The invention relates to heat engines, and more specifically, it deals with a heat engine speed governor.
2. Description of the Related Art
Among most important characteristics of engineering standards of a machine unit incorporating a heat engine are reliability, capacity, fuel consumption, quality of performance, fuming and toxicity of exhaust gases under transient conditions, operative involvement of a driver and force applied to the accelerator pedal, adaptivity of a heat engine to different fuel grades, mountainous conditions, subzero temperatures and other characteristics. All the above-listed characteristics depend to a large degree on static and dynamic characteristics of a heat engine speed governor.
Mechanical speed governors with a flyweight (more rarely pneumatic or hydraulic) sensor member are mainly used in existing heat engines, in particular in tractor and automobile diesel engines. In addition to the ensurance of high performance of heat engine speed control, such governors should form the external and part-load speed control characteristics of fuel supply with such an accuracy that power capabilities of a heat engine could be used to the maximum extent on the one hand and specific fuel consumption, temperature, fuming and toxicity of exhaust gases and other parameters of the heat engine should not reach critical values resulting in the impairment of the engineering standards of machine units on the other hand.
For forming external and part speed control characteristics of fuel supply, various kinds of correcting devices and mechanisms are installed in mechanical speed governors. To enhance automation of heat engine control and control of a machine unit as a whole, such speed governors are provided with special electrical actuators including a reversible electric motor for adjusting speed mode of a heat engine, electromagnets for limiting and interrupting fuel supply, an electromagnetic device for enriched fuel supply during starting of a heat engine, an electrohydraulic valve for shutting-off fuel supply in a fuel supply system for an emergency stop of a heat engine.
Also known in the art are electrical heat engine speed governors featuring a wide range of capabilities in enhancing automation of a heat engine control owing to the use of an integrated electrically actuated device for controlling position of a fuel metering member of a heat engine.
The type of program of operation of a speed governor, static, dynamic and functional properties incorporated therein depend on use of a machine unit, operating conditions, nature of load, kind of operations performed by the machine unit and on a number of other factors associated with different operations to be performed by the machine unit.
Known in the art is a large class of electrical heat engine speed governors built around a positioning electric actuator with an alternating direction of armature rotation, comprising an electric actuator proper which is operatively connected to a fuel metering member of a heat engine and electrically connected to a unit for comparing current value of the heat engine speed with the desired speed, a device for forming a program of a heat engine speed control, and a unit for forming an electric actuator control signal.
The electric actuator in such speed governors may be in the form of an electric torque motor or in the form of a proportional electromagnet (cf. Proc. of Symp. "R. Bosch", FRG. Ed. Moscow, May 16, 1984. K. Tsimmerman. Standards of Technology of "Bosch" Diesel Equipment (FIGS. 17 and 22), or in the form of a step motor (cf. Proc. Symp. "Friedman-Mayer" Austria. Ed. Leningrad, Apr. 16, 1984. F. Pashke. Development of Electronic Speed Governor. pp. 4, 5, FIG. 17). The above group of electric positioning actuators with alternating direction of armature movement during control will be hereinafter referred to as electric motors.
Process of speed control in a heat engine with the above-mentioned electrical speed governors occurs in the following manner. Under steady conditions, when a heat engine speed is equal to the desired speed, there is no signal at the output of the unit comparing these speeds. Consequently, the armature of the electric motor and a fuel metering member connected thereto are in an equilibrium position corresponding to the steady load of the heat engine. When current value of the heat engine speed deviates from the desired value, e.g. upon a change in load, a signal proportional to the difference between the compared speeds appears at the output of the comparison unit and is fed, via the electric motor control signal forming unit, to the electric motor. As a result, the fuel metering member is caused to move to a new position in which the values of current and desired speeds of the heat engine become equal.
Speed governors having an electric positioning actuator are characterized by a low level of utilization of output. This is due to the fact that under steady operating conditions of a heat engine, when the fuel metering member and the electric motor armature connected thereto remain stationary, the electric motor is in an almost braking mode of its armature which is characterized by a low efficiency. In addition, the alternating direction of magnetic flux of the armature of the electric motor and a hysteresis upon remagnetization of the armature caused thereby result in the appearance of a zone of its insensitivity to magnetic flux thus lowering accuracy of control of position of the fuel metering member so that dynamic characteristics of heat engine speed control are impaired (e.g. instability of speed, overshooting and transient time) and static characteristics, i.e. external and part-load speed control characteristics of fuel supply of a heat engine are impaired as well.
As operation of the above-described speed governors is based on the proportional control law, the external and part-load speed control characteristics of fuel supply are formed with a predetermined steepness at which a stable operation of the heat engine is ensured over the whole range of speed and load conditions. Upon a change in load of the heat engine, its speed will also change accordingly. The amount of load applied to the heat engine is assessed by a measured value of deviation of speed from the preceding value upon transition from one load mode of the heat engine to another. By feeding the measured signal to a device for forming a program of the heat engine control external and part-load speed control characteristics of fuel supply can be formed. It should be noted that because of the presence of a zone of insensitivity to magnetic flux in the electric motor, accuracy in forming such characteristics is low.
To enhance quality in forming static and dynamic characteristics, such speed governors are provided with an additional channel for controlling position of the fuel metering member. Measurement of position of the fuel metering member in this channel is carried out by means of an inductive position sensor (generally capacitance, photoelectric and other position sensors can be used as well) which is directly coupled to the fuel metering member and connected, via a converter, to a device for forming a heat engine control program. Therefore, a control signal in this control channel is formed in accordance with a linear parameter, and accuracy of measurement of such a parameter using such sensors is low because of a substantial measurement error. For this reason, even the provision of the channel for controlling position of the fuel metering member does not allow external and part-load speed control characteristics to be formed with the desired accuracy.
Also known in the art is a heat engine speed governor (SU,A, 708065), comprising a differential mechanism having a first input shaft operatively connected to a unidirectional electric motor, a second input shaft driven by a heat engine, and an output shaft operatively connected to a fuel metering member of the heat engine, a channel for electric motor speed control in which a means for measuring speed of the first input shaft of the differential mechanism is connected to an input of a device for forming a control signal having its output connected to the electric motor, and a master input connected to an output of a device for forming electric motor speed control program having an input for a setting signal, and a channel for correcting the electric motor speed in accordance with the heat engine speed, in which a means for measuring speed of the second input shaft of the differential mechanism has an output connected to an input of a differentiating unit having an output connected to a correction input of the device for forming a control signal in the electric motor speed control channel.
In this speed governor, the input shafts of the differential mechanism are caused to rotate in opposite directions by the heat engine and electric motor. With equal speeds of the shafts, the output shaft of the differential mechanism and the fuel metering member connected thereto remain stationary. Upon changes in load of the heat engine or preset speed of one of the input shafts, the output shaft rotates to move the fuel metering member to a position corresponding to the new load or speed mode of the heat engine so that speeds of the input shafts become equal again. The provision of the differential mechanism in this speed governor allows a unidirectional motor to be used rather than an alternating rotation motor. The main feedback in this speed governor is formed by the mechanical transmission from the heat engine shaft to the input shaft of the differential mechanism.
The above-described speed governor featuring high reliability, low electric motor power input and simple design ensures high dynamic performance in a heat engine speed control. This is due to the fact that speed of a heat engine with the employment of this speed governor and accuracy of speed maintenance are determined by a preset speed of the electric motor and accuracy of its stabilization in the electric motor speed control channel. To enhance quality of heat engine control in transient modes, the means for measuring speed of the second input shaft of the differential mechanism is connected to the correcting input of the device for forming a control signal via the differentiating unit.
This speed governor is based on an integrating control so as to be advantageous over the above-described types of speed governors. As this speed governor incorporates a unidirectional electric motor, there is no hysteresis with the unidirectional magnetic flux in its armature. This prevents a zone of insensitivity to magnetic flux from appearing in the speed governor as was the case with the above-described speed governors so that dynamic characteristics in a heat engine speed control are better. This speed governor also has enhanced static characteristics since external and part-load speed control characteristics of fuel supply feature a zero steepness which is especially desirable when a heat engine is to be used in such machine units as diesel-electrical units, agricultural tractors and combines, and transportation vehicles.
However, when a zero steepness of the speed control characteristics is ensured in fuel supply of a heat engine using such a speed governor, it is not possible to obtain information on load of the heat engine using a deviation of its speed, hence it is not possible to form external and part-load speed control characteristics in accordance with a law depending on load of the heat engine.